1. Field of the Invention
This invention relates to an acoustical measurement or estimation device, and particularly to a means to measure or to estimate the acoustical output of a loudspeaker connected to an electronic audio device (and measures the environmental sounds where appropriate) to determine the noise dosage, and as a means to determine the maximum allowable limit for the acoustical output of the electronic audio device, for reducing the possibility of noise induced deafness.
2. Background Art
Many people listen to audio music and other sounds via earphones or headphones connected to an electronic audio device such as home hi-fi sets and portable electronic audio devices. In recent times, portable electronic audio devices such as dedicated MP3 players, including iPods manufactured by Apple Inc, and similar players in multifunctional devices such as cellular phones, have gained popularity. FIG. 1A depicts how a typical electronic audio device 1 is used. The output of electronic audio device 1 is connected to earphone 3 by wire 2. Earphone 3 has a loudspeaker within its casing and is usually placed in concha 5 of the user's pinna (ear) 4. FIG. 1B depicts another common earphone 9, also sometimes called a earbud-type earphone (also sometimes called a earplug earphone), where rubber insert 8 is placed into the ear canal of the user and the loudspeaker is embodied within earphone casing 7. The loudspeaker is connected to electronic audio device 1 via interconnecting cable 2. In general, earbud-type earphone 9 provides some (ambient environmental) noise isolation compared to the more common earphone 3. In some instances, a headphone is worn over the user's pinna 4 instead of earphone 3 placed in concha 5 or earphone 9 in the ear canal.
FIG. 2 depicts the block diagram of a typical electronic audio device 1, comprising memory 20 where the recordings of the music tracks or other audio recordings reside, digital signal processor 21, digital-to-analog converter 22 that converts the digital output of digital signal processor 21 to an analog form that is amplified by audio amplifier 23. The electrical signal from audio amplifier 23 is converted to acoustical output in loudspeaker 24. Loudspeaker 24 is usually encapsulated within earphone 3 or 9 or within a headphone cup.
In many instances, the users of such an electronic audio device 1 set the output of digital signal processor 21 and/or audio amplifier 23 therein to a high electronic signal level such that loudspeaker 24 in earphone 3 or 9 or headphone produces loud (high volume) sounds, more specifically high acoustical intensity outputs, or equivalently high sound pressure levels.
It is well established that a person exposed to loud sounds over extended periods will likely suffer from permanent hearing impairment, in particular noise induced deafness. In industry, the allowable noise exposure of workers in many countries is established by their respective industry safety bodies. For example, in USA, the Occupational Safety and Health Association (OSHA) has established the number of hours and the associated sound intensity levels a person may be safely exposed to—computed as a noise dosage (also known as the Permissible (Noise) Exposure Level) and is usually measured by means of a noise dosimeter 30 in FIG. 3. Dosimeter 30 typically comprises measuring microphone 34 connected by cable 33 to the electronics enclosed in casing 31. The noise dosage may be displayed in display 32.
In general, the noise dosage is computed such that the higher the intensity of sounds (noise) that a person is exposed to, the shorter is the duration allowed. For example, under USA Occupational noise exposure (1910.95) for hearing conservation, a person exposed to a noisy environment of 90 dBA (decibels, A-weighted) is allowed to work in that environment for 8 hours, while a person exposed to noisy environment of 95 dBA is allowed to work in that environment for considerably shorter—4 hours. In environments where the noise levels are 90 dBA or higher, the worker typically wears hearing protectors to reduce his noise exposure such that his noise dosage remains within the stipulated noise dosage standards, thereby allowing the worker to work safely and longer in such noisy environments. In some countries, the limits are more stringent, for example, in the European Union, the limit is 80 dBA for 8 hours. These safety standards established by OSHA and other similar bodies are usually well observed by industry at large in developed countries.
To determine the noise dosage of a worker, microphone 34 of dosimeter 30 is typically clipped around the shoulder area, and the noise dosage is computed for ambient environmental sounds near the worker's pinna, more specifically at the entrance of the ear canal. Such prior-art noise dosimeters, however, cannot be used to measure the noise dosage from the acoustical output of loudspeaker 24 connected to electronic audio device 1. This is due to the mechanical incompatibility, inconvenience and the inappropriateness of these prior-art dosimeters.
This lack of a personal noise dosimeter is unfortunate because when a person wears earphones 3 or 9 or headphones connected to electronic audio device 1, the acoustical music and other sounds produced by loudspeaker 24 in earphones 3 or 9 or headphone constitute to the overall noise exposure of that person donning earphone 3 or 9 or headphone. As in an industrial setting where the environmental noise intensity levels may be high, the sound intensity levels produced by loudspeaker 24 in the earphone 3 or 9 or headphone may also be high. The acoustical output of loudspeaker 24 depends largely on the level of the signal output of audio amplifier 23 in electronic audio device 1 driving loudspeaker 24, the spectrum of the output electronic signal of audio amplifier 23, and the sensitivity (acoustical efficiency) of loudspeaker 24.
In terms of safety to mitigate the possibility of noise induced deafness (for hearing conservation), the noise dosage standards established by OSHA and similar bodies, would similarly apply to a person exposed to acoustical levels from loudspeaker 24 in earphone 3 or 9 or headphone. However, the actual dosage due to exposure of the user of electronic audio device 1 is largely the responsibility of the user as the acoustical output of loudspeaker 24 is controlled by the user. To this end, most manufacturers of electronic audio device 1 include an advice, warning or a disclaimer, informing the user of their electronic audio device 1 that exposure to high intensity sounds may result in hearing impairment and that users are advised not to exposure themselves to high intensity sounds over extended periods.
In short, a personal noise dosimeter to determine or to estimate the acoustical output and the ensuing noise dosage arising from loudspeaker 24 largely does not exist. Further, a personal noise dosimeter to determine or to estimate the noise dosage (and/or acoustical output) arising from loudspeaker 24 and from the ambient environment largely does not exist.
To assist users from exposing themselves to excessive high intensity sounds from their electronic audio devices 1, some manufacturers include features to limit the maximum signal output in their electronic audio device 1 by means of limiting the maximum output (for example 120 dB to 100 dB, and by means of automatic level control), thereby limiting the acoustical output from loudspeaker 24. This prior-at approach, although generally useful but the problem of excessive noise exposure remains largely because the maximum output is dependent on the level recordings of the music, type of music and that different people perceive different loudness and the noise dosage remains largely unknown.
In an industrial setting, a hearing protector is worn to reduce the noise dosage of the user. Typically, the noise exposure of the user is estimated by subtracting the Noise Reduction Rating (NRR) of the hearing protector from the ambient noise level. However, it is well known that the actual noise isolation or reduction from the hearing protector is highly variable and/or often over-estimated as the hearing protectors may not be properly worn, worn-out, damaged, and/or of than less-than-ideal fit. In some cases, the user wears earphone 3 or 9 under the hearing protectors to listen to music from electronic audio device 1 or there may be loudspeaker 24 within a ear cup of the hearing protector (connected to an audio system); the hearing protector may be a ear muff type, eartip, earplug or earplug-type earphone 9. This would likely increase the noise exposure of the user because other than the ambient environmental sounds, there is the added acoustical output from electronic audio device 1 or from an audio system.
In US Patent 2009/0208024, a microphone is placed at the outside of the enclosure of an apparatus (headset comprising a earplug) to measure the environmental sounds and output of a loudspeaker within the enclosure. As the input port of the microphone is placed contralateral (opposite) to the ear canal (i.e. outside the earplug, facing the environment), the noise exposure at the ear canal is estimated by the microphone readings and using the acoustic leakage path. Specifically, the environmental sounds at the ear canal is estimated by a direct measurement of the environmental sound attenuated by the earplug, while the acoustical sounds from the loudspeaker at the ear canal is measured by the same microphone after attenuation by the earplug. The attenuation of both measurements is estimated by the acoustic leakage path. This estimation of sounds from the environment and from the loudspeaker is crude because the acoustic leakage path needs to be precise. A precise acoustic leakage path (model) is unrealistic because of the varying ear canal sizes, imprecise and varying (due to movement) fit of the ear plug and if a reasonable earplug fit is obtained, the measurement of the loudspeaker output would be severely masked by the environmental sounds. In short, the measurement from this prior art invention (and ensuing noise dosage) is a crude estimation of the sound intensity at the ear canal, and likely to be highly imprecise and probably unacceptable; the present invention will offer a novel approach to circumvent these limitations.
In US Patent 2010/0278350, the noise dosimeter is obtained by means of a microphone that is placed in a dome-like structure that is inserted in the ear canal. Although this prior-art invention does provide a more precise means of ascertaining the noise dosage than that described in US Patent 2009/0208024, the microphone within the dome-like structure is cumbersome, intrusive, difficult to wear (insert) and may be uncomfortable, in part because the varying sizes of different ear canals.
In short, there is a need to precisely determine, by means of measuring or by estimating, the noise dosage from electronic audio device 1 and the like to prevent noise induced deafness, and the measurement/estimation needs to be convenient (easy to wear), comfortable and non-intrustive. This need is very pressing because at the present time, many teenagers already suffer mild sensorineural hearing impairment from extended use of electronic audio device 1 that is often set at high sound intensities. Note that a sensorineural hearing impairment is largely irreversible, and in some cases, tinnitus results. If extended use of audio electronic device 1 continues, the hearing impairment of the users of electronic audio device 1 would likely deteriorate to more severe sensorineural hearing impairment if their noise dosage is not controlled.
Hence, it is highly desirable to have a device that can conveniently and precisely measure or estimate the acoustical output of loudspeaker 24 of a earphone 3 or 9 or headphone (and ambient environmental sounds where appropriate), unlike prior-art methods that are imprecise, cumbersome, etc. The measured or estimated acoustical output is useful in a number of ways, including simply as a means to inform the user of the acoustical sound intensity, for computation of the noise dosage (also providing information to the user of the remaining allowable noise dosage and duration of use of electronic audio device 1), and as a means to determine the limit to set the maximum output of electronic audio device 1 (and loudspeaker output). The overall advantage is to reduce the possibly of hearing impairment (noise induced deafness) due to excessive noise exposure that many users of electronic audio devices suffer from and are unaware of.
It is also highly desirable to have a device that is able to simultaneously (directly or indirectly) measure the acoustical output of loudspeaker 24 of earphone 3 or 9 or headphone and measure the ambient environmental sounds where appropriate, without imprecise and complicated leakage paths or that heavily attenuates the signal to the microphone. This device will provide a true (or at least more precise than prior-art methods) noise dosage of the user, including in the case of a hearing protector.